Current optical storage devices use a light device to emit a light beam, such as a laser, to write data to and read data from optical recording media. Optical recording media include digital video discs (DVDs) and compact discs (CDs). To write data onto a disc, optical storage devices use the light beam to make a series of microscopic “marks” in a layer of the disc. The resulting sequence of light and dark marks (called “pits” and “lands”) represent the digital ones and zeros that comprise data. In rewritable optical storage devices, the light device creates “marks” by changing the reflective properties of a layer of the optical recording media. For example, the light beam produced by the light device may alter a portion of a phase-change alloy layer of the optical recording media from amorphous to crystalline, and vice versa. To read a disc, light is reflected off of the marks in the recording media back to the light device and read as information. The light device of rewriteable optical storage devices often includes two light emitting sources to produce two different light beams. One light beam is used to write data to the disc, while another less powerful light beam is used to read data from the disc.
Optical storage devices generally use a motor to spin discs to a certain number of revolutions per minute (RPM). The light device is affixed to floating head above the optical recording media. As the disc spins, the light beam is moved along the disc on the floating head and starts writing from the inner portion of the disc to the outside. Similarly, a light beam on the floating head moves across the disc to read data from the disc.
One drawback of conventional optical storage devices is that the amount of data that can be written to or read from an optical recording medium is limited by the size of the light beam emitted from the light device. This is because optical recording media have a finite amount of surface area over which marks can be formed. Therefore, it is desirable to make very thin marks to fit as many marks as possible on a disc. The width of the marks formed in the disc is governed by the diameter of the light beam. The diameter of the light beam is often referred to as “resolution.” The smaller the diameter of the light beam or the greater the resolution, the more marks can be fit onto the optical disc. Thus, more data can be packed onto the disc with the use of a more focused light beam having a narrow diameter or greater resolution.
However, the light devices used in conventional storage devices have a maximum resolution on the order of one wavelength due to the diffraction limit of light. That is, the diameter of the light beam can only be as small as the wavelength of the light used in the light beam. The diffraction limit is a fundamental maximum of the resolution of any optical system which is due to the diffraction of light. For example, a blue light beam of 470 nanometers (nm) can only have a resolution of 470 nm. As such, the amount of data that can be placed on optical recording media by conventional storage devices is inherently limited.
Moreover, the light beams produced by conventional storage devices must be placed in very close physical proximity to the optical recording media, in order to limit diffraction of the light beam. This close physical proximity of the light device to the recording media creates very low manufacturing tolerances. The precision with which conventional storage devices must be manufactured increases the costs of the devices.